Prior Art Statement
Several processes have been taught for the chlorination of bauxite and aluminum bearing clay. Dearborn in U.S. Pat. No. 1,605,098 and U.S. Pat. No. 1,600,216 teaches a two stage chlorination of bauxite and aluminum bearing clays. Both chlorination steps are done in the presence of a reducing agent and chlorine. Muggleton et al in U.S. Pat. No. 1,875,105 discloses chlorinating clays in the presence of carbon monoxide and chlorine at a temperature of 600.degree.-900.degree. C. to chlorinate the aluminum, iron and titanium. Thereafter, the residue is treated with carbon, chlorine and heat to chlorinate the silica and aluminum silicates contained in the clay. Staib in U.S. Pat. No. 1,866,731 discloses treating raw material containing aluminum and silicic acid with a carbonaceous material and equal parts of chlorine and silicon tetrachloride in order to chlorinate the aluminum and not the silica contained in the material. Nowak et al in U.S. Pat. No. 3,244,509 utilizes a reductive chlorination followed by an oxidative chlorination, both performed at 800.degree.-1200.degree. C., to extract iron from iron oxide bearing materials. Chlorine need not be present for either chlorination step and carbon is the preferred reducing agent for the reductive chlorination step. Nowak in U.S. Pat. No. 3,466,169 chlorinates ores in a reducing-oxidizing atmosphere while regulating the amount of added chlorine to correspond stoichiometrically to the metal having the greatest chloride-forming affinity.
With the exception of leaching processes, none of the prior art teaches a satisfactory process for economically recovering aluminum from clays associated with coals or from bauxite having the required purity for commercial sale because of the difficulty of separating the aluminum from other metals present in these materials, particularly, iron. Separation through the chlorination route to recover aluminum as aluminum chloride looks attractive; however, the process must produce an aluminum chloride of substantial purity. For example, purity requirements for aluminum chloride feed material to an Alcoa-type aluminum cell are reported to limit the Fe.sub.2 O.sub.3 content of the feed to 0.03 percent. Furthermore, in the chlorination process, the chlorination of unwanted metals, such as silicon, must be suppressed to restrict the consumption of chlorine; otherwise, the process becomes prohibitively expensive.
A further problem involved in recovering the metal values from clays through the chlorination route, is the disposal of alkali and alkaline earth metal chlorides remaining in the final residue.
Accordingly, it is a principal object of this invention to provide a method for recovering aluminum of substantially high purity from bauxite and clays associated with coal which contain iron and siliceous material with the aluminum.
It is another object of this invention to provide a method for suppressing the chlorination of siliceous material when recovering aluminum as aluminum chloride from clays and bauxite by chlorination.
It is a further object of this invention to provide a method for the disposal of alkali and alkaline earth metal chlorides remaining in the final residue resulting from the chlorination of clays to recover aluminum as aluminum chloride.